Dang, that's a call every diesel driver dreads. Bummer. How long was it driven, and did any dash lights come on? Any chance you can get it scanned without it being started accidentally? If you don't have a VAG-specific scanner, in the US I'd be expecting DTCs like P0087, P0088, and P0191 ... not sure if those are the same in the UK.
Given your engineering background, I'm sure you know the biggest issue is lack of lubrication from petrol. Without a scanner, I'd be looking for anything obvious around the HPFP/injectors/N290 Fuel Metering Valve.
The issue is, you need a scanner pretty much no matter what. After draining the fuel, you will want to use VCDS to activate the in-tank lift pump for several minutes to prevent the HPFP from running dry during the initial start-up after a tank/system flush. There is a VW TSB out there that goes over how a dealer would do it, and it's intense and they replace the fuel pump as well as purge the system more than once. Depending on mileage and condition, those kinds of drastic repairs may not be plausible.
You should do your own research and see what's available in your region and recommended for your engine, but I've ran Archoil AR6500 through for extra lubricant addidives after fuel contamination and it gave me peace of mind if nothing else. A similar product is Opti-Lube XPD.
stop the engine or did the engine stop by itself before she realized what had happened?
